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In film, it is called density. On the computer, it is called __________.
Brightness
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Two photographic factors that allow detail to be seen:
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Typical OD range
.25 - 2.5
.25 is lower density; whiter
2.5 is higher density, darker
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Instrument used to measure density.
Densotometer
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What is density?
variations of darkness; the black and white
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When changing density, do you use window level or window width?
window level
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What is the main controlling factor of density?
mAs (mass)
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3 Lightening techniques:
Bright "hot" lights - higher intensity; higher amps (higher numbers) means more light penetrating
- Digital optical scanner - adjust the settings
- Duplication (copying)
- an older machine reprints the film lighter/darker
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main elements of the body that the x-ray interacts with:
hydrogen (water component, body tissue, low atomic #)
oxygen (water component, body tissue, low atomic #)
calcium (bone, high atomic #)
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Does increasing mAs increase or decrease density?
Increasing mAs increases density.
Decreasing mAs decreases density.
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What is the "rule of thumb" when increasing mAs to change density?
Double it to increase, Half it to decrease
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How much of a change is needed, in mAs, before a change in density is discernible to the naked eye?
a 30% change.
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If you need to increase the kVp by a certain percent, how do you go about it (mathematically)?
multiply the kVp by the percent needed with a 1. in front of it.
Example: to increase 15%, multiply by 1.15
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If you need to decrease the kVp by a certain percent, how do you go about it (mathematically)?
multiply the kVp by the number you would add to the percent amount to make it equal 100, but with a decimal point in front.
- Example: decrease 15%, multiply by .85
- Example: decrease 60%, multiply by .4
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What type of radiation are we using? What is special about it?
We use x-ray radiation. It is an ionizing radiation.
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What is the main influencing factor of density?
kVp
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To change the density by changing the kVp, what is the generalized rule for increments?
Change in 15% increments...the 15% rule
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generators, listed from weakest energy to strongest energy:
- single phase
- 3-phase, 6-pulse
- 3-phase, 12-pulse
- high frequency
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Changing the kVp changes the ______ of the beam.
energy
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If you have good technique on a high frequency machine, what would you have to do if you changed to a single phase machine?
You would have to increase your technique since it's a weaker beam. It would need increased power to show the same image as well as a stronger machine.
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Define Blooming.
causing pixel size to become larger than the nominal or state size; a distortion
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Describe the expected influence of the focal spot on density when the unit has been properly calibrated.
There should be no difference between large and small focal spots.
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What is the anode heel affect?
An effect that alters the intensity of radiation (and therefore the density) between the anode and cathode ends of the x-ray tube.
up to 45% difference depending on the angle of the anode
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Which end always has greater image receptor exposure, the cathode end or the anode end?
the cathode end, by up to 45%. it gets "hotter"
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The patient's head is located on the ______ side, and the feet are located on the _______ side.
head: anode
feet: cathode
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Towards the cathode side, the density is ________.
Greater (up to 45%)
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SID is short for:
Source-to-image receptor distance
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What is the SID conversion formula?
- mAs1 (SID1)2
- ____= ____
- mAs2 (SID2)2
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Inverse Square Law
- The law affects exposure in inverse proportions to the square of the distance.
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As an example of the inverse square law, if you re exposed to 400mR of scatter radiation when 1 ft away from your patient, how much radiation are you exposed to if you move to 2 ft away from your patient? 4 ft away?
- 100mR at 2ft
- 25mR at 4 ft
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In this class...what will we always do with distance when it comes to formulas?
Square anything to do with distance!!
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When distance increases, density ____________.
decreases
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When collimation increases, density __________.
decreases
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When field size increases, density __________.
increases
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When beam restriction increases, density __________.
decreases
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As field size decreases, intensity ___________.
decreases (exposed to less photons)
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Increased filtration will ____________ density.
decrease
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Filtration ___________ overall average energy of the beam.
increases
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As tissue thickness increases, film density __________.
decreases
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What happens as the atomic number of tissue gets higher?
The tissue absorbs more of the x-ray, allowing less x-ray to pass through to the film. Therefore, the film density is less where there is tissue with high atomic number, making it look lighter. Bone is an example of tissue with a high atomic number.
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Where is the highest atomic number in the body?
the teeth (because of the enamel)
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Tissue type is affected by which 2 main factors?
- the average atomic number
- the density of the tissue
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Does denser tissue increase or decrease density on the film?
decrease
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You may have to __________the density when making large tube angles.
increase
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In pathology, an additive __________ density and creates an effect called __________.
additive: decreases density and is radiopaque.
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In pathology, a destructive _________ density and creates an effect called _________.
destructive: increases density and is radiolucent.
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Example of an Additive:
Fluid in the lungs (pneumonia)
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Example of a Destructive:
Emphysema
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When grid ratio increases, density ___________.
decreases
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Grid advantage/disadvantage
- advantage: absorbs scatter; less reaches film
- disadvantage: increases exposure to patient
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Grid Conversion Formula
- GCF1 mAs1
- ____ = ____
- GCF2 mAs2
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What is the GCF if there is no grid?
1
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What is the GCF for the Grid ratio of 5:1?
2
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What is the GCF for the grid ratio of 6:1?
3
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What is the GCF for the grid ratio of 8:1?
4
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What is the GCF for the grid ratio of 10:1?
5
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What is the GCF for the grid ratio of 12:1?
5
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What is the GCF for the grid ratio of 16:1?
6
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Consider using a grid once the part being x-rayed reaches _______ in size.
10cm
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Calcium is high in what type of absorption?
photo-electric absorption
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When Relative Speed (RS) increases, density ________.
increases
-
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With the same technique, which would show the greater density, a pediatric cassette or a regular cassette?
pediatric cassette
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With the same technique, which would show the greater density, a regular cassette or a fine detail cassette?
regular cassette
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When film processing time increases, density __________.
increases
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When film processing temperature increases, density __________.
increases
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When chemical activity increases, density __________.
increases
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Describe the "formula reminder" for how to calculate density when working with mA and time.
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